Adverse Mental Health Effects of Cannabis Use in Two Indigenous Communities in Arnhem Land, Northern Territory, Australia: Exploratory Study

Abstract

Objective: We investigated adverse mental health effects and their associations with levels of cannabis use among indigenous Australian cannabis users in remote communities in the Northern Territory. Method: Local indigenous health workers and key informants assisted in developing 28 criteria describing mental health symptoms. Five symptom clusters were identified using cluster analysis of data compiled from interviews with 103 cannabis users. Agreement was assessed (method comparison approach, κ-statistic) with a clinician's classification of the 28 criteria into five groups labelled: ‘anxiety’, ‘dependency’, ‘mood’, ‘vegetative’ and ‘psychosis’. Participants were described as showing ‘anxiety’, ‘dependency’ etc., if they reported half or more of the symptoms comprising the cluster. Associations between participants' self-reported cannabis use and each symptom cluster were assessed (logistic regression adjusting for age, sex, other substance use). Results: Agreement between two classifications of 28 criteria into five groups was ‘moderate’ (64%, κ=0.55, p<0.001). When five clusters were combined into three, ‘anxietydependency’, ‘mood-vegetative’ and ‘psychosis’, agreement rose to 71% ( κ=0.56, p<0.001). ‘Anxiety-dependency’ was positively associated with number of ‘cones’ usually smoked per week and this remained significant when adjusted for confounders (p=0.020) and tended to remain significant in those who had never sniffed petrol (p=0.052). Users of more than five cones per week were more likely to display ‘anxiety-dependency’ symptoms than those who used one cone per week (OR=15.8, 1.8–141.2, p=0.013). A crude association between the ‘mood-vegetative’ symptom cluster and number of cones usually smoked per week (p=0.014) also remained statistically significant when adjusted for confounders (p=0.012) but was modified by interactions with petrol sniffing (p=0.116) and alcohol use (p=0.276). There were no associations between cannabis use and ‘psychosis’. Conclusions: Risks for ‘anxiety-dependency’ symptoms in cannabis users increased as their level of use increased. Other plausible mental health effects of cannabis in this population of comparatively new users were probably masked by alcohol use and a history of petrol sniffing.